This invention relates to a two-speed accessory drive mechanism which is capable of rotating engine driven accessories at either of two predetermined speeds. More particularly, the invention relates to a drive which includes wear compensating means such that the response time during subsequent activations of the drive remains relatively constant regardless of the periodic wearing of the components of the drive.
It is well known that engine driven accessories generate a parasitic drag upon the engine, thereby reducing its over-all efficiency. A two-speed accessory drive permits the optimum utilization of these accessories by selectively operating them at one of two predetermined speeds which are selected as a function of engine speed. Operating the accessories in this manner increases their longevity and reduces the parasitic drag upon the engine. One form of accessory drive incorporates within a single, crankshaft driven unit, a clutching device which often uses a planetary gear set which, upon selective activation, operates the accessories attached thereto through a belt at either of the two operating speed. Such gear units produce an audible whine and are relatively lengthy in order to accommodate the internal gearing mechanisms.
It is an object of the present invention to provide a drive or drive system characterized by smooth, quiet engagement in response to gear-motor activation. A further object of the present invention is to provide such a system utilizing a one way roller clutch wherein the overrunning speed of the clutch is decreased in comparison to the overrunning speed of prior devices. An additional object of the present invention is to provide a system having a wear compensation means, thereby providing repeatable engagement time to activate the system.
The present invention comprises a drive system comprising an input member, an output member, and friction clutch means movable in a first direction to cause engagement and in an opposite or second direction to cause disengagement of the input and the output members. The system further includes means isolated from the input member, responsive to control signals for moving the clutch means in the first and second directions; and control means for generating a first control signal to cause the clutch means to move in the first direction, thereby engaging the output member to the input member and including wear compensation means for generating a second control signal to cause the clutch means to move in the second direction by a fixed amount, thereby disengaging from the output member.
Many of the features, purposes and objects of the invention will be clear from the detailed description of the drawings.